drm/i915/guc: Always enable the breadcrumbs irq

The execlists emulation on top of the GuC (used for scheduling and
preemption) depends on the MI_USER_INTERRUPT for its notifications and
tasklet action. As we always employ the irq, there is no advantage in
ever disabling it while we are using the GuC, so allow us to arm the
breadcrumb irq when enabling GuC submission and disarm upon disabling.
The impact should be lessened by the delayed irq disabling we do (we
only disable after receiving an interrupt for which no one was wanting),
but allowing guc to explicitly manage the irq in relation to itself is
simpler and prevents an issue with losing an interrupt for preemption
as it is not coupled to an active request.

Internally, we add a reference counter (breadcrumbs.irq_enabled) as a
simple mechanism to allow GuC to keep the breadcrumb irq enabled. To
improve upon always enabling the irq while guc is selected, we need
to hook into the parking facility of intel_engines so that we only enable
the breadcrumbs while the GT is active (one step better would be to
individually park/unpark each engine).

In effect, this means that we keep the breadcrumb irq always enabled for
the entire duration the guc is busy, whereas before we would try to
switch it off whenever we idled for more than interrupt with no
associated waiters. The difference *should* be negligible in practice!

v2: Stop abusing fence signaling (and its auxiliary data structures) to
enable the breadcrumbs irqs.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>,
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>,
Link: https://patchwork.freedesktop.org/patch/msgid/20171025143943.7661-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -523,29 +523,6 @@ static void i915_guc_submit(struct intel_engine_cs *engine)
 	}
 }
 
-static void nested_enable_signaling(struct drm_i915_gem_request *rq)
-{
-	/* If we use dma_fence_enable_sw_signaling() directly, lockdep
-	 * detects an ordering issue between the fence lockclass and the
-	 * global_timeline. This circular dependency can only occur via 2
-	 * different fences (but same fence lockclass), so we use the nesting
-	 * annotation here to prevent the warn, equivalent to the nesting
-	 * inside i915_gem_request_submit() for when we also enable the
-	 * signaler.
-	 */
-
-	if (test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-			     &rq->fence.flags))
-		return;
-
-	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags));
-	trace_dma_fence_enable_signal(&rq->fence);
-
-	spin_lock_nested(&rq->lock, SINGLE_DEPTH_NESTING);
-	intel_engine_enable_signaling(rq, true);
-	spin_unlock(&rq->lock);
-}
-
 static void port_assign(struct execlist_port *port,
 			struct drm_i915_gem_request *rq)
 {
@@ -555,7 +532,6 @@ static void port_assign(struct execlist_port *port,
 		i915_gem_request_put(port_request(port));
 
 	port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
-	nested_enable_signaling(rq);
 }
 
 static void i915_guc_dequeue(struct intel_engine_cs *engine)
@@ -1097,6 +1073,16 @@ static void guc_interrupts_release(struct drm_i915_private *dev_priv)
 	rps->pm_intrmsk_mbz &= ~ARAT_EXPIRED_INTRMSK;
 }
 
+static void i915_guc_submission_park(struct intel_engine_cs *engine)
+{
+	intel_engine_unpin_breadcrumbs_irq(engine);
+}
+
+static void i915_guc_submission_unpark(struct intel_engine_cs *engine)
+{
+	intel_engine_pin_breadcrumbs_irq(engine);
+}
+
 int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
 {
 	struct intel_guc *guc = &dev_priv->guc;
@@ -1154,6 +1140,9 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
 		execlists->irq_tasklet.func = i915_guc_irq_handler;
 		clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
 		tasklet_schedule(&execlists->irq_tasklet);
+
+		engine->park = i915_guc_submission_park;
+		engine->unpark = i915_guc_submission_unpark;
 	}
 
 	return 0;
@@ -1168,6 +1157,8 @@ void i915_guc_submission_disable(struct drm_i915_private *dev_priv)
 {
 	struct intel_guc *guc = &dev_priv->guc;
 
+	GEM_BUG_ON(dev_priv->gt.awake); /* GT should be parked first */
+
 	guc_interrupts_release(dev_priv);
 
 	/* Revert back to manual ELSP submission */

drivers/gpu/drm/i915/i915_irq.c

@@ -1068,6 +1068,9 @@ static void notify_ring(struct intel_engine_cs *engine)
 	struct drm_i915_gem_request *rq = NULL;
 	struct intel_wait *wait;
 
+	if (!engine->breadcrumbs.irq_armed)
+		return;
+
 	atomic_inc(&engine->irq_count);
 	set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 
@@ -1101,7 +1104,8 @@ static void notify_ring(struct intel_engine_cs *engine)
 		if (wakeup)
 			wake_up_process(wait->tsk);
 	} else {
-		__intel_engine_disarm_breadcrumbs(engine);
+		if (engine->breadcrumbs.irq_armed)
+			__intel_engine_disarm_breadcrumbs(engine);
 	}
 	spin_unlock(&engine->breadcrumbs.irq_lock);
 

drivers/gpu/drm/i915/intel_breadcrumbs.c

@@ -123,7 +123,7 @@ static void intel_breadcrumbs_fake_irq(struct timer_list *t)
 	 */
 
 	spin_lock_irq(&b->irq_lock);
-	if (!__intel_breadcrumbs_wakeup(b))
+	if (b->irq_armed && !__intel_breadcrumbs_wakeup(b))
 		__intel_engine_disarm_breadcrumbs(engine);
 	spin_unlock_irq(&b->irq_lock);
 	if (!b->irq_armed)
@@ -171,15 +171,37 @@ void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 
 	lockdep_assert_held(&b->irq_lock);
 	GEM_BUG_ON(b->irq_wait);
+	GEM_BUG_ON(!b->irq_armed);
 
-	if (b->irq_enabled) {
+	GEM_BUG_ON(!b->irq_enabled);
+	if (!--b->irq_enabled)
 		irq_disable(engine);
-		b->irq_enabled = false;
-	}
 
 	b->irq_armed = false;
 }
 
+void intel_engine_pin_breadcrumbs_irq(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock_irq(&b->irq_lock);
+	if (!b->irq_enabled++)
+		irq_enable(engine);
+	GEM_BUG_ON(!b->irq_enabled); /* no overflow! */
+	spin_unlock_irq(&b->irq_lock);
+}
+
+void intel_engine_unpin_breadcrumbs_irq(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock_irq(&b->irq_lock);
+	GEM_BUG_ON(!b->irq_enabled); /* no underflow! */
+	if (!--b->irq_enabled)
+		irq_disable(engine);
+	spin_unlock_irq(&b->irq_lock);
+}
+
 void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
@@ -241,6 +263,9 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
 	struct intel_engine_cs *engine =
 		container_of(b, struct intel_engine_cs, breadcrumbs);
 	struct drm_i915_private *i915 = engine->i915;
+	bool enabled;
+
+	GEM_BUG_ON(!intel_irqs_enabled(i915));
 
 	lockdep_assert_held(&b->irq_lock);
 	if (b->irq_armed)
@@ -252,7 +277,6 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
 	 * the irq.
 	 */
 	b->irq_armed = true;
-	GEM_BUG_ON(b->irq_enabled);
 
 	if (I915_SELFTEST_ONLY(b->mock)) {
 		/* For our mock objects we want to avoid interaction
@@ -273,14 +297,15 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
 	 */
 
 	/* No interrupts? Kick the waiter every jiffie! */
-	if (intel_irqs_enabled(i915)) {
-		if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
-			irq_enable(engine);
-		b->irq_enabled = true;
+	enabled = false;
+	if (!b->irq_enabled++ &&
+	    !test_bit(engine->id, &i915->gpu_error.test_irq_rings)) {
+		irq_enable(engine);
+		enabled = true;
 	}
 
 	enable_fake_irq(b);
-	return true;
+	return enabled;
 }
 
 static inline struct intel_wait *to_wait(struct rb_node *node)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -339,9 +339,9 @@ struct intel_engine_cs {
 		struct timer_list hangcheck; /* detect missed interrupts */
 
 		unsigned int hangcheck_interrupts;
+		unsigned int irq_enabled;
 
 		bool irq_armed : 1;
-		bool irq_enabled : 1;
 		I915_SELFTEST_DECLARE(bool mock : 1);
 	} breadcrumbs;
 
@@ -848,6 +848,9 @@ unsigned int intel_engine_wakeup(struct intel_engine_cs *engine);
 #define ENGINE_WAKEUP_WAITER BIT(0)
 #define ENGINE_WAKEUP_ASLEEP BIT(1)
 
+void intel_engine_pin_breadcrumbs_irq(struct intel_engine_cs *engine);
+void intel_engine_unpin_breadcrumbs_irq(struct intel_engine_cs *engine);
+
 void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine);
 void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine);